Tutor profile: David M.
Subject: Organic Chemistry
Why are phenols more acidic than alcohols?
When an acid dissociates in water, it releases hydronium (or H+) ions. When a compound is more likely to release H+, the more acidic it is. In the case of phenols and alcohols, phenols are more likely to release H+ because the resulting phenoxide ion (the conjugate base of phenol) is resonance-stabilised. This means that the negative charge is delocalised in the aromatic ring; the conjugate base is more likely to form. On the other hand, alcohols do not give H+ ions easily to form alkoxide ions; they are unstable and readily take H+ ion and form alcohol again.
Why does adenine combine with thymine only and not cytosine?
The rules of base pairing (or nucleotide pairing) are: A with T: the purine adenine (A) always pairs with the pyrimidine thymine (T) C with G: the pyrimidine cytosine (C) always pairs with the purine guanine (G) This rule is known as "Chargaff's rule". This complementary pairing is generally based on the formation of hydrogen bonds of the bases with each other to form the DNA double-helix structure. Adenine forms two hydrogen bonds with thymine and cytosine binds with guanine with three hydrogen bonds.
Subject: Basic Chemistry
Why does water boil at a high temperature (100 C)?
Water has a high boiling point because the water molecules are held by significant strong forces called hydrogen bonding. To overcome these forces, a significant amount of heat (or kinetic energy) is required.
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